Hi,
The default Export of Orders as a csv file I get 146 columns.
That's understandable
I'm seeking to use just four of those columns (ideally) .... order_created, order_invoice_number, order_full_price, order_full_tax
If that's what you want to do, then these are not chooks teeth.
I think you just went with a wrong path. Instead of trying to do this with reports, you want to do this with a mass action.
Go in the menu System>Mass actions, create a new mass action of the type "order", and add an action "export CSV file". There, select these columns order_created, order_invoice_number, order_full_price, order_full_tax.
Then, when you click on the "process" button of the mass action, you'll get a CSV file with only these columns.
Note that by default, it will export all the orders.
If you want to filter based on the date of the orders, you'll want to add filters to your mass action on the order_created column. You can use unix timestamps, or use operations on the {time} tag.
For example, you could have a filter on the order_created column with the operation >= and the value: {time}-2592000
2592000 is the number of seconds in 30 days, so that means it will only export orders of the past 30 days.